Generally, an antenna is to radiate a radio wave to a free space or receive the radio wave. The antenna may be generally classified into a linear antenna, an aperture antenna, a micro strip antenna, a planar horn array antenna, a reflector antenna, a lens antenna, etc., based on various classification standards.
The radio wave radiated from the antenna has a predetermined pattern. Here, a polarization of the radiated radio wave is classified into a linear polarization, a circular polarization, an elliptical polarization, etc., depending on a direction in which an electric field or a magnetic field vibrates and a direction in which a wave proceeds.
In this case, the circular polarization among the polarizations of the radio wave radiated from the antenna is a radio wave in which a locus of a vector end representing a magnitude and a direction of the electric field draws a circle on a plane vertical to the radio wave direction. Generally, the circular polarization may be divided into two linear polarization components which have the same amplitude, polarization planes orthogonal to each other, and different phases by 90°. However, when the amplitudes of the two linear polarization components are different from each other, a composite wave draws an elliptical shape on the plane vertical to the radio wave direction, which is called an elliptical polarization. Meanwhile, in the circular polarization or the elliptical polarization, clockwise rotating the electric field vector of the plane vertical to the radio wave direction toward the radio wave direction is called a clockwise elliptical polarization and counterclockwise rotating the electric field vector of the plane vertical to the radio wave direction toward the radio wave direction is called a counterclockwise elliptical polarization.
The planar horn array antenna means an antenna having a lot of antenna elements arranged therein to control a phase of an excitation current of each element and form a main beam having a by allowing an antennal to have a specific direction and the same phase and is mainly used as an automatic directional antenna for a satellite, etc.
However, a plurality of communication satellites are densely arranged above the equator now, and therefore signal interference occurs between adjacent communication satellites even when the signals from the planar horn array antenna are transmitted to the preset communication satellites.
To solve the above problems, a method for reducing a signal output level of the planar horn array antenna and allocating more frequencies thereto has been used. However, the method has a problem in that a transmission speed of the signal from the planar horn array antenna may be reduced and a rental fee of the communication satellite may be increased.
FIG. 1 is a graph illustrating a beam pattern of a typical planar horn array antenna.
As illustrated in FIG. 1, upon designing the typical planar horn array antenna, an array interval of each element needs to be equal to or more than λ/2 due to a problem of a conduit interference in the antenna. When the array interval of the elements is equal to or more than λ/2, there is a problem in that a grating lobe (GL) occurs. A beam pattern of the radio wave is beyond an off-axis mask (OAM) to cause interference between the adjacent communication satellites.
To solve the above problems, Korean Patent Laid-Open Publication No. 2008-0105856 discloses a dual linear polarization horn array antenna, which may reduce a size of the antenna but may not solve the grating lobe occurring from the planar horn array antenna.
Further, the planar horn array antenna has elevation angles and skew angles changed depending on locations and therefore products and specifications of the planar horn array antenna need to be determined in consideration of the skew angles and the elevation angles of each location.
The skew angle means a difference between a receiving angle of a low noise blockdown converter (LNB) and a transmitting angle of a satellite and is also changed depending on the location since the earth is round.
For example, a latitude and a longitude of Perth city which is the western district of Australia each are 31° S and 115° E and a latitude and a longitude of Canberra of the eastern district which is a capital of Australia are 35° S and 149° E. Upon calculating each skew, Perth city has a skew angle of −50° and Canberra has a skew angle of −15°, and therefore the difference in the skew angle therebetween is considerably large.
Therefore, to overcome the difference in the skew angle on each location, the planar horn array antenna needs to control the skew angle as needed. However, for the planar horn array antenna to control the skew angle, the planar horn array antenna needs to mechanically rotate, which leads to a problem in that the planar horn array antenna is complicated, takes up much space, and has reduced accuracy.